A cementitious composition gains maximum mechanical performance properties such as compressive, flexural and tensile strengths after about 28 days cure. Cementitious compositions made with low water/cement ratio will have good water resistance if they are properly placed and cured. Cementitious compositions for mortar applications, which have high water/cement ratio and are used in thin applications, suffer from a loss of strength and adhesion characteristics when exposed to water permeation/absorption.
It is known in the art that the water absorption or waterproofing properties of a cementitious composition can be affected by incorporating additives such as paraffin, pozzolanic materials and metal salts of fatty acids absorbed on inert filler. These additives are also referred to as damp proofing or permeability reducing agents. Such commercial water resistance additives provide only marginal improvement in water resistance while adversely affecting the strength development properties. Their use in cementitious compositions increases mixing water demands which results in a decrease in mechanical performance properties such as compressive, tensile and flexural strengths. Some water repellent additives work well in reducing water absorption, but they retard the cement hydration reaction and also migrate to the exposed surface of the mortar. In such cases, the finishing coating of synthetic emulsion displays poor adhesion to the mortar surface.
U.S. Pat. No. 4,434,257 discloses a cement composition having improved crack resistance and water resistance which comprises a mixture of a conventional cement composition with an ethylene-vinyl acetate copolymer emulsion containing 1-10 parts by weight of a polyvinyl alcohol and 0.1-10 parts by weight of a higher fatty acid ester of a polyvalent alcohol having an HLB of 10 or less per 100 parts by weight of the solid resin components of the emulsion. It is stated that when the ester has an HLB of more than 10, the desired improvement of properties of the product cannot be achieved. Preparation 18 which uses a polyoxyethylene sorbitan trioleate with an HLB of 11 is shown in Table I to provide inferior water resistance compared to the preparations according to the invention.
U.S. Pat. No. 3,537,869 discloses additives for cementitious mixtures capable of increasing the compressive strength of the hardened product by 25 to 125%, the additives being various partial fatty acid esters.